Marco was a teenaged boy, and he lived in a very crowded house. Stinky smells were hardly a deterrent for him. He was intrigued, more than anything, when he saw the creature. He didn't know what it was, or that it was actually one of the town residents somehow transformed, though he knew that was happening in town at the moment.
He approached with caution, because be tended to be overly cautious at times. Especially when Star wasn't around. Or maybe more so when she was because she didn't know the meaning of the word. He was alone at the moment, he didn't even have Barko or Nachos with him. So he was being cautiously cautious.
"Hi." He waved a hand, hoping to appear friendly to the creature.